a blog about Networks and Places

Always Green Traffic Control

Nick Musachio, local inventor in Minnesota, has just been issued a patent (No. 8,711,005) for his Always Green Traffic Control System. (Since this is transportation, we will abbreviate this AGTCS)

Imagine you have an isolated signalized intersection, operating near but below capacity. If vehicles were able to travel at the correct speed when approaching the intersection for a significant distance, they should be able to travel through the intersection without hitting a red light or being delayed by standing queues. If at 45 MPH they would hit a red light, but at 35 MPH would get a green, they should be informed to reduce speed to 35 MPH. This not only reduces driver delay, but should decrease crashes and decrease emissions, both of which are exacerbated by intersection control and braking and acceleration.

How would drivers know which speed to travel? An upstream Variable Message Sign with Dynamic Speed Limits (tied into the traffic signal controller cabinet, or with the pre-programmed traffic signal timings) would tell them the best speed to avoid stopping. If only the first car in a platoon does this (on a 1 lane road), all following cars are controlled by default.

Audi has a similar in-vehicle system. That is only useful if the traffic agencies produce live feeds of traffic signal timings. Comment: it is appalling that such a traffic signal timing live feed doesn’t generally exist (even transit agencies, not historically known for their cutting edge research) have GTFS.

AGTCS is infrastructure based, and works for all vehicles anywhere an agency wants to set it up.

3 thoughts on “Always Green Traffic Control”

A system like this was proposed in the 1970’s by a Pierre Jomini who was a signal engineer in Colorado and later Montana. It was called a speed funnel. The dynamic signs were intended to compress random flow into a platoon that would arrive at the signal on green. The two major issues were; a background cycle had to be superimposed on what was a free running actuated signal in order to create predictability since the sign would likely need to be more than a cycle length from the signal and then does the roadway operating agency feel comfortable telling a driver to drive 30 mph or more below the posted speed limit? Another issue was accounting for queue discharges times at the signal when the light turned green.

Pierre said that a speed funnel was deployed in Switzerland on a low speed roadway with a 2 phase signal and a short cycle.

SRF Consulting Group, while completing a study of providing truck priority at signals for MnDOT in 2002, included the speed funnel as one alternative. The speed funnel was modeled in Vssim, but with the restriction that the sign would not display below 40 mph in a 55 mph zone. The fixed back ground cycle added delay to the side street and left turns and also increased the number of vehicles in the “dilemma zone” on the high speed mainline during the yellow change interval. It was not pursued.

In the late 1990’s SRF was also doing a project for the Iowa DOT in Muscatine. There was a proposal to create a signal ITS laboratory and the speed funnel was one item that was planned to be tested. However, funding never was obtained.

For coordinated actuated signals along a corridor, Econolite controllers are capable of providing an output to drive a sign that would tell drivers that they are in the coordination band (or hard part of the green) as opposed from having a soft green because the minor moves ended early. To my knowledge no one is actually using that feature.

Even back in the 1950’s some coordinated signal systems, with fixed cycle lengths, had changeable signs that displayed the progression speed associated with that coordination plan. Some pre-timed systems even had static signs that read “Signals Set For XX mph”.

There is an intersection in Herndon, VA that actually does the opposite. If you are speeding on the approach, it will turn the signal red. I have seen similar systems in Spain.

Thanks for the wonderful history Dennis. I think you are the source of the traffic funnel report I got from Eric Minge at SRF. It made me less lonely reading about their pioneering attempts. They were on the right path, but didn’t quite solve the riddle. I did. That’s the difference.

As to drivers not wanting to slow down. The system modeling shows that in the two lanes using conventional signals over 2700 cars per hour stop. With my system about 40 stop. Additionally, as Dr. John Hourdos pointed out, “you don’t need 1005 compliance. Once the first cars comply the followers have no choice.” The further from the light and the shorter the cycle, the less speed reduction is necessary.

The difference between this system and the speed funnel are that this system gives precise speeds to follow resulting in a more precise landing in front of the about to turn signal. The speed funnel rounded to the nearest ten, which is pretty imprecise and would result in forming multiple platoons, and driver conflict as the signals change from one speed to the next.

This system does work with actuated signals -if the actuation happens during a precise time window. My contention all along, has been that in with the increase our attempts at “real time dynamic response to traffic” has only lead to more randomness and chaos. The proof is all around us.